1. Field of the Invention
The present invention relates to a technology for manufacturing a substrate comprised of a very tiny circuit pattern, such as a semiconductor devices and a liquid crystal. More particularly, the present invention relates to a charged-particle beam inspection technology for inspecting the tiny circuit pattern using a charged-particle beam.
2. Description of the Related Art
Semiconductor devices are fabricated by repeating a step of transferring a pattern, which is formed on a wafer using a photo mask, through lithography or etching. In such a fabrication process, for quick boost of a yield and realization of stable running of the fabrication process, it is a must to quickly analyze a defect, which is discovered by performing in-line wafer inspection, for the purpose of taking measures on the basis of the results of the analysis. In order to link the results of the inspection to a countermeasure to defectives, a technology for quickly reviewing numerous detected defects and classifying them by a cause is needed.
However, due to the decrease of a design rule of semiconductor manufacturing process, the size of a defect affecting a fabrication yield of a semiconductor device is decreasing. A conventional optical review apparatus has difficulty in reviewing and classifying microscopic defects because of an insufficient resolution. Consequently, a scanning electron microscope (SEM) type review apparatus capable of reviewing defects at a high resolution has come to be adopted. In the review apparatus, acquisition of a shadow image based on an SEM image which is equivalent to a shadow caused by light incident from side of an object to be reviewed is important in detecting a roughness such as a microscopic foreign matter or a scratch.
A general principle for acquisition of the shadow image will be described in conjunction with FIG. 1. When an roughness 1 caused by a foreign matter included in a film is scanned with an electron beam 2, a secondary particle 3 is emitted from each irradiated point on a sample. The generated secondary particle 3 has a distribution with respect to the energy. A component of a relatively low energy (low-velocity component) is referred to as a secondary electron (SE), while a component of a relatively high energy (high-velocity component) is referred to as a backscattering electron (BSE). As indicated with arrows 6 in FIG. 1, a secondary particle at a generational position at which the secondary particle is generated has elevation-angle components oriented in various directions. Here, the elevation angle of a secondary particle at a generational position means an angle formed by each elevation-angle component of the secondary particle with respect to a plane to which the optical axis of an irradiated primary electron beam is normal. As far as a certain elevation-angle component 6 of a secondary particle at a generational position is concerned, components of the secondary particle emitted rightward reach a detector 4 but components thereof emitted leftward do not reach the detector. Therefore, the quantity of a secondary electron detected by the detector 4 varies depending on a level of a slope 5 of a sample surface at the generational position of a secondary particle. Consequently, a shadow contrast depending on an roughness on a sample surface is appeared in a shadow image 7 obtained by the detector.
Disclosed in Japanese Patent Application Laid-Open No. 8-273569 is an invention relating to a charged-particle beam column in which a secondary charged particle detection optical system using a magnetic/electrostatic compound objective lens, accuracy of measurement is improved by detecting a low-velocity component (SE) and a high-velocity component (BSE) in a secondary particle distinctively. In the invention disclosed in the publication, an annular detector disposed between an electron source and an objective lens is utilized, and the backscattering electron is detected in an internal annular zone of the annular detector, and the secondary electron is detected in an external annular zone of the annular detector, on the basis of the fact that trajectories of the low-velocity component and high-velocity component of a secondary particle are different, thus the separation and detection of the secondary particle is achieved by. The external annular zone is divided into four sectors so that a specific azimuth component of a secondary electron at a position from which the secondary electron is emitted can be distinguished. Consequently, a shadow image can be acquired.
On the other hand, disclosed in PCT Publication No. WO00/19482 is a configuration for distinguishing and detecting a low-angle component and a high-angle component of a secondary particle. In the invention disclosed in the publication, a secondary particle detector for detecting the low-angle component is disposed above an objective lens, and a reflector to which the low-angle component of a generated secondary particle collides is disposed between the low-angle component detector and objective lens. Further, an incidental particle generated from the collision of the low-angle component is introduced into the low-angle component detection secondary particle detector using an ExB deflector, whereby the low-angle component of a reflected electron and a secondary electron are detected. For the high-angle component of the reflected electron, another high-angle component detection secondary particle detector and a second ExB deflector are disposed above the ExB deflector (on the side of the electron source) so that the high-angle component detector can detect the high-angle component alone.
Moreover, disclosed in Japanese Patent Application Laid-Open No. 2006-228999 is an electron microscope in which an annular detector is disposed between an electron source and an objective lens so that a low-elevation angle component and a high-elevation angle component of a generated secondary electron can be separated from each other and an azimuth component can be separated from the secondary electron.